Frequency modulated single point fuel injection circuit with duty cycle modulation

Abstract

A frequency modulated control circuit for an electronic fuel injection system to control the pulse-type injection of fuel at a single point of the fuel intake of an internal combustion engine in accordance with the derived mass air flow rate into the engine comprising a pressure sensor for sensing the manifold pressure of the internal combustion engine, and an engine speed sensor, both of which generate an analog signal which are multiplied by a multiplier circuit to provide a signal representative of the mass air flow to the engine. The multiplier circuit includes a separate control input for varying the output signal level of the multiplier circuit by a preselected factor determined by the final output of the control circuit. The output of the multiplier circuit is fed to a voltage controlled oscillator to produce an output signal taking the form of a pulse train, the frequency of which varies with the amplitude of the mass air flow signal. The output of the voltage controlled oscillator is fed to a pulse generator which generates a fixed on-time pulse for each pulse in the pulse train being fed from the voltage controlled oscillator. The output of the pulse generator is sensed by a duty cycle switch which senses when the output frequency of the voltage controlled oscillator results in a high duty cycle for the output pulses. In this high duty cycle situation, the output analog signal of the multiplier is reduced by a preselected fraction. The duty cycle switch also generates an output signal which varies the duration of the pulse output from the pulse generator as a reciprocal of the variation being applied to the multiplier from the duty cycle switch or enable a secondary injector. The system also includes a temperature sensor and coolant temperature circuit which generates an analog voltage signal which varies as a function of the engine coolant temperature. The temperature analog signal, designated V H .sbsb.2 O , is fed to a cold start circuit to control the output pulse width fromn the cold start circuit.

I claim: 
     
       1. A frequency modulated fuel injection system for internal combustion engines comprising: pressure sensing means for measuring the manifold pressure of the engine and generating a pressure electrical signal representing said manifold pressure;   means responsive to the rotational speed of the engine and generating a speed electrical signal representing said rotational speed;   function generating means responsive to said pressure and speed electrical signals for generating a control signal directly proportional to both said pressure and speed electrical signals;   means for generating a reference signal;   oscillator means connected in responsive relation to said function generating means and said reference signal generating means for generating a variable frequency electrical signal in response to said control signal and said reference signal;   pulse generator means connected to said frequency modulated electrical signal for generating an electrical pulse signal having a variable duty cycle in response to the frequency of said variable frequency signal; and   injection means connected to said pulse generator means and operative in response to said electrical pulse signal for supplying the fuel demand to the engine.   
     
     
       2. The frequency modulated system of claim 1 wherein said pulse is of fixed on-time duration and variable off-time. 
     
     
       3. In the frequency modulated fuel injection system according to claim 1 wherein said injection means comprises at least one fuel injection valve positioned at the inlet of the intake manifold system of the engine and operative in response to said electrical pulse signal to supply the fuel demand to all the cylinders of the engine. 
     
     
       4. The frequency modulated system of claim 1 wherein said control signal is proportional to the product of said pressure and speed electrical signals. 
     
     
       5. The frequency modulated system of claim 4 wherein said control signal is an analog function of the product of said pressure and speed electrical signals. 
     
     
       6. The frequency modulated system of claim 5 wherein said reference signal generating means includes means for sensing the temperature of the internal combustion engine, said reference signal being proportional to said temperature. 
     
     
       7. The frequency modulated system of claim 6 wherein said temperature reference signal varies as a direct function of said temperature. 
     
     
       8. The frequency modulated system of claim 1 additionally including duty cycle switch means responsive to the frequency of said electrical pulse signal from said pulse generator means and operative to modify the pulse width of said electrical pulse signal from said pulse generator means. 
     
     
       9. The frequency modulated system of claim 8 wherein said duty cycle switch is connected to receive the output of said function generating means and modify said control signal. 
     
     
       10. The frequency modulated system of claim 9 wherein said duty cycle switch reduces the frequency of said variable frequency signal when the ratio of said pulse width to the time between pulses exceeds a predetermined value. 
     
     
       11. The frequency modulated system of claim 1 additionally including engine temperature sensing means including means generating an electrical signal in response to engine temperature, and cold start means responsive to said electrical signal generated by said engine temperature responsive means for generating a cold start electrical pulse signal having a predetermined pulse width and a pulse repetition rate proportional to the magnitude of said engine temperature electrical signal generated by said engine temperature responsive means. 
     
     
       12. The frequency modulated system of claim 11 further including means for electrically connecting said cold start electrical pulse signal to said injector means. 
     
     
       13. The frequency modulated system of claim 11 wherein said means for electrically connecting said cold start electrical pulse signal to said injector means operates to electrically add the frequencies of said cold start electrical pulse signal and said frequency modulated electrical signal from said pulse generator means thereby increasing the amount of fuel being supplied to the engine. 
     
     
       14. The frequency modulated system of claim 11 further including means for generating a cranking signal, and wherein said means for supplying said cold start electrical pulse signal is activated by an electrical cranking signal indicating engine cranking and is deactivated by the absence of said cranking signal. 
     
     
       15. The frequency modulated system of claim 14 further including means for connecting said cranking signal generating means to at least one of said oscillator means or said pulse generator means for inhibiting said oscillator or pulse generator means. 
     
     
       16. A fuel injection system for an intenal combustion engine comprising: at least one fuel injector means for injecting fuel demand to the engine;   means responsive to the manifold pressure of the engine for generating a pressure electrical signal having an amplitude proportional to said manifold pressure;   means responsive to the speed of the engine for generating a speed electrical signal having an amplitude proportional to the speed of the engine;   means for multiplying said pressure and speed electrical signals from said manifold pressure means and said speed means generating a product electrical signal wherein the amplitude is proportional to a predetermined direct relationship between said pressure and speed electrical signals;   amplitude controlled oscillator means responsive to said product electrical signal for generating an electrical signal having a frequency proportional to said amplitude of said product electrical signal; and   pulse generator means responsive to said electrical signal from said oscillator means for generating a frequency modulated pulsed electrical signal having a fixed pulse width and a pulse repetition rate equal to the frequency of said oscillator means, said frequency modulated pulsed electrical signal connected to said fuel injector means for operating the fuel injection means and supplying the fuel demand to the engine.   
     
     
       17. The fuel injection system of claim 16 wherein said oscillator means is a voltage controlled oscillator. 
     
     
       18. The fuel injection system of claim 16 additionally including means responsive to the temperature of the engine for generating an engine temperature electrical signal having an amplitude proportional to the temperature of the engine, said engine temperature electrical signal modifying the frequency of said oscillator means. 
     
     
       19. The fuel injection system of claim 18 wherein said engine temperature electrical signal modifies the frequency of said oscillator directly as the amplitude of said engine temperature electrical signal. 
     
     
       20. The fuel injection system of claim 18 additionally including means for generating an electrical signal indicating initiation of engine cranking; and   cold start signal generating means responsive to the amplitude of said engine temperature electrical signal and said engine cranking signal for generating a frequency modulated pulsed electrical signal for operating the fuel injection means for supplying additional fuel flow to the engine, said frequency modulated pulsed electrical signal having a fixed pulse width and a pulse repetition rate proportional to said frequency modulated pulsed electrical signal.   
     
     
       21. The fuel injection system of claim 16 wherein said means for multiplying is adopted to receive a plurality of electrical signals and to generate an output signal which is the product of said input signals. 
     
     
       22. The fuel injection system of claim 16 wherein said fuel injector means is located at a common point for all cylinders of the engine thereby providing a single point frequency modulated fuel injection system. 
     
     
       23. The fuel injection system of claim 16 further including duty cycle switch means responsive to the frequency of said frequency modulated pulsed electrical signal from said pulse generator means and operative to increase the pulse width of said frequency modulated pulsed electrical signal from said pulse generator means and to simultaneously reduce the frequency of said frequency modulated pulsed electrical signal when the ratio of said pulse width to the time between pulses exceeds a predetermined value. 
     
     
       24. The fuel injection system of claim 23 wherein said fuel injector means is located at a common point for all cylinders of the engine thereby providing a single point frequency modulated fuel injection system. 
     
     
       25. The fuel injection system of claim 24 further including a secondary injector, said secondary injector being enabled in response to a signal from said duty cycle switch. 
     
     
       26. A frequency modulated fuel injection system for internal combustion engines comprising: pressure sensing means for measuring the manifold pressure of the engine and generating a pressure electrical signal representing said manifold pressure;   means responsive to the rotational speed of the engine and generating a speed electrical signal representing said rotational speed;   multiplying means responsive to said pressure and speed electrical signals for generating an analog signal proportional to a function of said pressure and speed electrical signals;   means for generating a reference signal;   oscillator means responsive to said analog signal and said reference signal for generating a frequency modulated electrical signal;   pulse generator means connected to said frequency modulated electrical signal for generating an electrical pulse signal having a predetermined duty cycle depending upon the frequency of said frequency modulated signal;   injection means operative in response to said electrical pulse signal for supplying the fuel demand to the engine; and   duty cycle switch means responsive to the frequency of said electrical pulse signal from said pulse generator means and operative to modify the pulse width of said electrical pulse signal from said pulse generator means.   
     
     
       27. The frequency modulated system of claim 26 wherein said duty cycle switch is connected to receive the output of said multiplier means and modify said analog signal. 
     
     
       28. The frequency modulated system of claim 27 wherein said duty cycle switch reduces the frequency of said frequency modulated signal when the ratio of said pulse width to the time between pulses exceeds a predetermined value. 
     
     
       29. A fuel injection system for an internal combustion engine comprising: at least one fuel injector means for injecting fuel demand to the engine;   means responsive to the manifold pressure of the engine for generating a pressure electrical signal having an amplitude proportional to said manifold pressure;   means responsive to the speed of the engine for generating a speed electrical signal having an amplitude proportional to the speed of the engine;   means for multiplying said pressure and speed electrical signals from said manifold pressure means and said speed means generating a product electrical signal wherein the amplitude is proportional to a predetemined relationship between said pressure and speed electrical signals;   oscillator means responsive to said product electrical signal for generating an electrical signal having a frequency proportional to said amplitude of said product electrical signal;   pulse generator means responsive to said electrical signal from said oscillator means for generating a frequency modulated pulsed electrical signal having a fixed pulse width and a pulse repetition rate equal to the frequency of said oscillator means said frequency modulated pulsed electrical signal for operating the fuel injection means for supplying the fuel demand to the engine; and   duty cycle switch means responsive to the frequency of said frequency modulated pulsed electrical signal from said pulse generator means and operative to increase the pulse width of said frequency modulated pulsed electrical signal from said pulse generator means and to simultaneously reduce the frequency of said frequency modulated pulsed electrical signal when the ratio of said pulse width to the time between pulses exceeds a predetermined value.   
     
     
       30. The fuel injection system of claim 29 wherein said fuel injector means is located at a common point for all cylinders of the engine thereby providing a single point frequency modulated fuel injection system. 
     
     
       31. The fuel injection system of claim 30 further including a secondary injector, said secondary injector being enabled in response to a signal from said duty cycle switch. 
     
     
       32. A frequency modulated fuel injection system for controlling the operation of a fuel injector in an internal combustion engine comprising: pressure sensing means for measuring the manifold pressure of the engine and generating a pressure signal representing said manifold pressure;   means responsive to the rotational speed of the engine and generating a speed signal representing said rotational speed;   multiplying means responsive to said pressure and speed signals for generating a control signal proportional to a function of said pressure and speed signals;   oscillator means responsive to at least said control signal for generating a frequency modulated signal in response to said control signal;   pulse generator means connected to said frequency modulated signal for generating a pulse signal having a predetermined duty cycle depending upon the frequency of said frequency modulated signal for controlling the fuel injector in response thereto; and   duty cycle switch means responsive to the frequency of said pulse signal from said pulse generator means and operative to modify the pulse width of said pulse signal from said pulse generator means.